Determination of the quadrupole splitting of the first excited state of 119Sn in β-tin by the e- -γ TDPAC technique

It is shown that for the determination of the quadrupole splitting (ω₀ = 28.5 ± 1.0 MHz) of the first excited 23.8 keV state of ¹¹⁹Sn in β-tin the e^- -γ time-differential perturbed angular correlation technique is superior to the Mössbauer method.     

Experiments on the search for the effect of resonant screening on the probability of Mössbauer absorption of <Superscript>119<Emphasis Type="Italic">m</Emphasis></Superscript>Sn gamma rays

Experiments on the search for the effect of resonant screening on the Mössbauer absorption of ^119m Sn γ rays of energy 23.8 keV emitted by a standard Mössbauer Ca^119m SnO₃ γ source in the resonant SnO₂ absorber of natural isotopic composition are described. Intensities of tin γ rays and X-rays that passed through the absorber were measured with and without a resonant cylindrical screen (which was a black absorber for the 23.8-keV Mössbauer γ line) around the absorber and their ratios were calculated for each radiation separately. No difference beyond the experimental error was found between these ratios measured with the γ source both at rest and when oscillating with a frequency and amplitude enough to completely break the conditions for Mössbauer resonant absorption of 23.8-keV γ rays. The upper limit for the relative decrease, due to the influence of the resonant screen, in the intensities of these γ rays after their passing through the resonant absorber was 0.00030.     

Magnetic dipole moments of excited states of105Pd and other spectroscopic investigations in the decay of105g Ag

The IPAC-method has been used with the external magnetic field of 9.0 T of a split coil superconducting magnet and with the internal field of PdFe for a measurement of magnetic moments of¹⁰⁵Pd states populated in the decay of 41.29d¹⁰⁵Ag. The results are:μ _7/2 (645 keV)=?1.49(9) nmμ _5/2 (319 keV)=+0.95(20) nmμ _3/2 (280keV)=?0.074(13) nm. The half-life of the 645 keV state has been redetermined by use of cooled thallium free Nal detectors asT _1/2 (645 keV)=126(2) ps. γ-γ directional correlations were measured with a system of three large Ge planar diodes for the cascades 443–645 keV, 332–319 keV, 393–280 keV, and 64–280 keV and analyzed in terms of dipole quadrupole mixing ratios of theγ-lines involved. The spin of the 673 keV state was derived as l/2⁺.     

High-resolution resonance study of the12C+n total cross section in the region of13CT=3/2 states

The¹²C+n total cross section has been studied in the region of the lowestT=3/2 states of¹³C. The firstT=3/2 state at (15108.2±1.2) keV excitation is observed as a weak resonance anomaly. The deduced resonance parameters agree with previous results. At higher excitation energies four sharp anomalies have been observed at (17534±3) keV, (18082±3) keV, (20057±4) keV and (21703±4) keV excitation with total widths between 12 keV and 20 keV. The results are discussed with respect to a possibleT=3/2 assignment. An upper limit of the elasticity (J+1/2) Γ_no/gG is deduced for thoseT=3/2 levels which do not appear as resonance anomalies.     

Threshold states in 26Al revisited

Threshold states in ²⁶Al have been re-examined using the ²⁷Al(³He, α)²⁶Al and ²⁵Mg(³He, dγ)²⁶Al reactions in order to resolve apparent ambiguities in some of the previously reported properties of these states. In particular, the s-wave resonance strength reported at E_c.m. = 37 keV is now found to be located at E_c.m. = 57.54 keV, and the proton width for the 374 keV resonance has been revised to Γ_p = 0.82 eV. These results have been used to calculate a new resonance strength of ωγ = 1.6 × 10⁻¹³ eV for the 57.54 keV resonance. As a result, the stellar production rate for ²⁶Al is increased by a factor ∼- 3–38 for temperatures T₉ = 0.05–0.1.     

Der Zerfall des125m Xe,des127m Xe und des127g Xe

The decay of^125m Xe produced by the reaction¹²²Te(α, n)^125m Xe using a target enriched in¹²²Te (95.4%) and the decay of^127m Xe produced by the reaction¹²⁷J(d, 2n)^127m Xe have been investigated: ^125m Xe decays with a half-life ofT _1/2=(56±3) sec by ayy- cascade withE _γ1=(140.4 ±0.5) keV andE _γ2=(110.5 ±0.5) keV. The experimental conversion coefficients yield multipolarities ofE3 for the 140.4 keV isomeric transition and predominantlyM1 for the 110.5 keV-transition. ^127m Xe decays with a half-life ofT _1/2=(71±2) sec. The decay also proceeds by aγγ-cascade with an isomeric E3 transition ofE _γ1=(172.5±0.3) keV and a predominantlyM1 transition ofE _γ2=(124.6±0.3) keV. In the decay of^127g Xe an additional branching of the electron capture to a level at (618.1±0.3) keV was observed. The relative probability forK-captureP _K618/P_K375=0.40 ±0.07 yields a total transition energyQ _EC=(664 ±4)keV. A spin of 1/2⁺ was assigned to the ground state.     

The gamma decay of analogue states in61Cu

Resonances in the reaction⁶⁰Ni(p, γ)⁶¹Cu have been studied in the proton energy rangesE _p=1840–1880 keV and 2220–2300 keV. Decay schemes and branching ratios have been determined for a number of resonances, three of which are identified as analogue fragments of the 283 keV (1/2^?) and 656 keV (3/2^?) states in⁶¹Ni. The split analogue components of the 283 keV state atE _x≈6.6 MeV are seen to decay significantly to a group of states in the region of excitation 3–4 MeV. Gamma ray angular distributions yield the following resonance spins:E _p=2248 keV,J=3/2;E _p=2263 keV,J=5/2. Also, the⁶¹Cu ground stateβ ⁺ decay to parent levels in⁶¹Ni has been compared to the respective analogue stateM1 gamma decay to the⁶¹Cu ground state.     

States of167Ho from the decay of neutron rich nuclide167Dy

Theβ ^?-decay of ₆₆ ¹⁶⁷ Dy produced through the fast neutron reaction¹⁷⁰Er(n, α)¹⁶⁷Dy has been investigated by using several kinds of detectors and a high-capacity two-parameter recording system. The half-life andβ ^?-decay energy of¹⁶⁷Dy were determined to beT _1/2 = 6.20 ± 0.08min andQ _β-=2.35±0.06, respectively. The observed level scheme of ₆₇ ¹⁶⁷ Ho (completely unknown previously) contains 12 states, among them a 6.0±0.1 μsM2 isomer at 259.3 keV. On the basis of theoretical and systematic considerations combined with multipole determinations, the following Nilsson model assignments are proposed for the lowest states of¹⁶⁷Ho: 0 keV (7?/2 [523]), 259.3 keV (3+/2[411]), 319.8 keV (5/2 3+/2[411]), 392.5 keV (1+/2[411]), 410.0 keV (3/2 1+/2[411]), 569.7 keV (3?/2{7?/2[523], 2⁺}). Theβ-decay proceeds mainly to the proposed gamma-vibrational state at 569.7 keV with an anomalously low logft value 5.4, indicating similarity between the microscopic structures of this state and the famous ¦K ₀?2¦ gamma vibration of¹⁶⁵Ho.     

Measurement of radiation energy by spectrometric systems based on uncooled silicon detectors

The results of measurements of radiation energy for single-channel detection systems based on uncooled silicon planar detectors and spectrometric readout electronics, developed at the Kharkiv Institute of Physics and Technology National Scientific Center, are presented. Radiation sources of ⁵⁵Fe, ²⁴¹Am, ⁵⁷Co, ¹³⁷Cs, and ^99MTc and characteristic X-ray radiation (CXR) are used in the experiments. The radiation energy in the range of E _γ = 3–140 keV is measured by a spectrometer based on a Si PIN detector. The energy resolution (full width at half maximum, FWHM) in this energy range changes with increasing photon energy from 0.97 to 1.3 keV. The CXR of calcium (K _α = 3.69 keV) is measured by a Si planar detector with an input aluminum foil. Emission lines in the energy range of E _γ = 0.04–0.662 MeV are measured by a CsI(Tl) scintillator-silicon PIN-photodiode detection system. The energy resolution of the spectrometer changes with quantum energy increasing from 22 to 70 keV. The CXR from cesium and iodine with K _α 31 and 28.6 keV, respectively, is recorded.     

Derp 3/2-Analogzustand in51V

In an investigation ofT=7/2 analogue states in⁵¹V the⁵⁰Ti(p, γ) excitation curve has been measured for proton bombarding energies 1280–1480 keV and 2340–2660 keV. From the (p, γ) resonances 29 new virtual levels in the region of 9316–9510 keV excitation energy in⁵¹V were determined. The strong resonance atE _p=1 371 keV has been identified as the isobaric analogue state of the⁵¹Ti ground state by determining spin and parity of this resonance to be 3/2^?. There is no evidence for a strong analogue resonance in⁵¹V corresponding to the 1.16 MeV _{p 1/2} state in⁵¹Ti. The γ-decay of the _{p 3/2} analogue state has been studied by measuring branching ratios and angular distributions of primary γ-transitions with a Ge(Li) detector.M1E2 mixing ratios have been determined for these transitions. The total width of the resonance for γ-decay is found to be Γ_γ=1.6±0.4 eV. New bound levels in⁵¹V have been introduced at 3576, 4651 and 4661 keV excitation energy. TheJ ^π values of the 3085, 4770, and 4863 keV states are determined to be 5/2^?, 5/2^?, 3/2^?, respectively. The analogue-antianalogueM1 transition strength is found to be considerably reduced compared to the situation ins-d shell nuclei.     

Untersuchung des Zerfalls von134Cs durch γ-γ-Winkelkorrelationsmessungen

γ-γ-angular correlation measurements with Ge(Li) detectors and NaJ(Tl) detectors provided theE2/M1 mixing ratios of the following gamma transitions: 3 ₁ ⁺ →2 ₂ ⁺ (475.3 keV), 2 ₂ ⁺ →2 ₁ ⁺ (563.3 keV), 4 ₂ ⁺ →4 ₁ ⁺ (569.4 keV), 3 ₁ ⁺ →2 ₁ ⁺ (1,039 keV). The angular correlation measurements were only consistent with spin 3 of the 1,643 keV level. The half life of the 1,401 keV level was determined by delayed coincidence techniques to beT _1/2 (1,401 keV)≦30 ps.     

Multipole mixing ratios of transitions in168Er

Time-integral and time-differentialγ-γ directional correlation measurements were performed for cascades in¹⁶⁸Er populated from the electron-capture decay of¹⁶⁸Tm(87d). The¹⁶⁸Tm source was dissolved in HF acid to minimize extranuclear perturbations. The results of the time-differential experiment for the 448-99.3 keV and 448-198 keV cascades showed agreement with time dependent interaction and gaveλ ₂(1094)=(0.79±0.09) ×10⁷ sec^?1. The attenuation factors for the 80 keV level were determined asG ₂₂ (80)=0.90±0.01 and G₄₄(80)=0.94±0.01. OnlyI=4 spin value for the 1094 keV level is consistent with our measurements. The 632, 731, 741, and 816 keV transitions connecting theK=2⁺ andK = 0⁺ rotational bands were found to be of almost pureE2 character. The 99.3, 198, 547, 720, 830, and 1277 keV transitions are of practically pureE1 multipolarity. The 448 keVMl transition has (0.8 _?0.4 ^+2.0 )%E2 admixture. The results for the 1014?80keV cascade give (23±4)%E3 component in the 1014 keV transition.     

Isomer shifts and changes of the nuclear charge radii in99Ru and101Ru

The recoilless nuclear gamma resonance of the 127 keV γ-rays of¹⁰¹Ru was observed in ruthenium metal, RuO₂ and [Ru(NH₃)₄(HSO₃)₂]. By comparison of the isomer shifts observed in these materials for the 127 keV absorption line with the corresponding shifts of the 90keV γ-rays of⁹⁹Ru one obtains δ〈r ²〉 [127 keV]/ δ〈r ²〉 [90 keV]=1.78±0.26 for the ratio of the changes of the mean square nuclear charge radii between the first excited and the ground states in these nuclei. An estimate of electron density differences based on free-ion relativistic self-consistent field calculations yields δ〈r ²〉[90keV]≈+1.4·10^?3 for⁹⁹Ru and δ〈r ²〉/〈r ²〉 [127 keV]≈+2.4·10^?3 for the¹⁰¹Ru case. These results are discussed in terms of the core excitation model.     

Investigation of the effect of resonant environment (Mössbauer screen) on the observed half-life of the 119m1Sn isomer (E = 23.8 keV, T 1/2 ∼ 18 ns)

In order to analyze the effect of resonant environment on the γ decay of excited nuclei, the half-life of the ^119m1Sn isomer (E = 23.8 keV, T _1/2 ～ 18 ns), which appears from the decay of the ^119m2Sn state (E = 89 keV, T _1/2 ～ 293 d), has been measured by the e-γ coincidence method on samples consisting of the mixture of tin oxides containing the ¹¹⁹Sn stable nucleus and ^119m2Sn radioactive nuclei with various values of the ¹¹⁹SnO₂/^119m2SnO₂ ratio. For the samples, where this ratio is equal to 6.2 × 10⁴, 1.2 × 10⁶, 6.5 × 10⁶, and 1.7 × 10⁷, the half-life T _1/2is equal to 18.69(2), 18.71(2), 18.91(5), and 19.43(4) ns, respectively. For the reference sample (a metal with a ¹¹⁹Sn/^119m2Sn ratio of 1.5 × 10⁵), the value T _1/2 = 18.68(6) ns is obtained.     

Energy loss of deuterons in 3He gas: a threshold effect

The energy loss of deuterons in ³He gas was measured at E _d = 15 to 100 keV using the ³He pressure dependence of the ³He(d,p)⁴He cross-section at a given incident energy. At the highest energies, the observed energy loss is in good agreement with a standard compilation. However, with decreasing energy the experimental values drop steadily below the theoretical values and near E _d = 18 keV they drop sharply (within 1 keV) reaching the domain of nuclear stopping power. This threshold behavior is due to the minimum 1s → 2s electron excitation of the He target atoms, i.e. it is a quantum effect. Some consequences are discussed.     

Mössbauer effect study of hyperfine interactions in145Nd

The magnetic hyperfine splitting of the 72.5 keV γ rays of¹⁴⁵Nd was investigated in intermetallic compounds of Nd and in the paramagnetic salts Nd _x Y _1-x Cl₃·6H₂O (withx=0.02 andx=0.05) at 4.2 K. With the magnetic hyperfine tensorA of Nd_0.01Y_0.99Cl₃·6H₂O known from EPR spectroscopy, the analysis of the unresolved magnetic hyperfine spectra yieldsI _e =5/2 for the spin of the 72.5 keV state, in contradiction to a previous result. The multipolarity of the 72.5 keV γ transition was found to be essentiallyM1 with δ²=0.010±0.014, and the magnetic moment of the 72.5 keV state was determined as μ(5/2)=?0.319±0.004 nm. For various divalent and trivalent Nd compounds as well as for metallic Nd the isomer shift IS of the 72.5 keV γ line was measured. A value for the change of the mean square nuclear charge radius during the 72.5 keV γ transition of Δ〈r ²〉=+(1.9±0.9)·10^?3fm² was deduced using electron density differences from free-ion Hartree-Fock calculations.     

Das Quadrupolmoment des 2,3 MeV-Zustandes in120Sn

Time differentialγγ-angular correlation measurements have been performed to determine the electric interaction of the 2.3 MeVI=5^? state of¹²⁰Sn in different polycristalline antimony compounds. A calibration of the field gradient was achieved by Mößbauerexperiments with the 23.8 keVI=3/2⁺ state in¹¹⁹Sn using identical sources. From the ratio of the measured electric interactions the ratio of the quadrupole moments is deduced as: $$\left| {\frac{{Q(2.3{\mathbf{ }}MeV level,{\mathbf{ }}I = 5^ - ,^{120} Sn)}}{{Q(2.8{\mathbf{ }}keV level,{\mathbf{ }}I = {3 \mathord{\left/ {\vphantom {3 2}} \right. \kern-\nulldelimiterspace} 2}^ + ,^{119} Sn)}}} \right| = 2.86(15)$$ . Using 0.06 (2) b for the quadrupole moment of the 23.8 keV level in¹¹⁹Sn one gets for the quadrupole moment of the 2.3 MeV level in¹²⁰Sn ¦Q(2.3 MeV level,I=5^?,¹²⁰Sn)¦=0.021 (8) b.     

Investigation of gamma-ray transitions in56Ni

Angular correlation measurements for the⁵⁴Fe(³He,n γ)⁵⁶Ni reaction were performed at \(E_{3_{He} } = 12.5\) MeV. Method II of Litherland and Ferguson was used to determine the multipole mixing ratio of theγ-radiation and the spins of the excited levels at 3925 and 3956 keV. As the most probable spin assignments we deduced 4⁺ (3925 keV) and 0⁺ (1,2) (3956 keV). The mixing ratio found for the 1225 keV transition from 4⁺→2 ₁ ⁺ isδ(M3/E2)=+0.21 _?0.16 ^+0.23 This result is compared with a shell model calculation.     

Der radioaktive Zerfall des Fe61

Fe⁶¹(T _1/2=5.95 min) was produced irradiating Ni⁶⁴ and natural nickelfoils with fast neutrons in the reaction Ni⁶⁴(n, α)Fe⁶¹; Fe was chemical seperated. The gamma and beta spectrum were investigated with Ge(Li)-counters, NaJ(Tl) and plastic scintillation spectrometers. Fe⁶¹ emits five gamma rays having the energies and intensities per Fe⁶¹ decay: 121 keV (0.064), 177 keV (0.027), 298 keV (0.293), 1025 keV (0.461), 1202 keV (0.539). Threeγγ-cascades could be identified: 121–177 keV, 121–1202 keV, 298–1025 keV. Inγ β-coincidence measurements the maximal beta energy was determined:E _βmax=2.86 MeV. A decay sceme Fe⁶¹-Co⁶¹ was constructed: Fe⁶¹, spin and parityJ ^π=3/2^?, decays by means of allowed beta decay to three excited states of Co⁶¹: 1323 keV (1/2^?), 1202 keV (3/2^?), 1025 keV (5/2^?). The energies and intensities per Fe⁶¹ decay of the three beta decay modes are: 2.56 MeV (0.367), 2.68 MeV (0.495), 2.86 MeV (0.138). — A 88 keV gamma ray (T_1/2=33 sec) was observed coming from the Co⁶³ decay.     

Decay properties of the 19/2− isomers in113,117Sb

By means of the generalized centroid-shift method, the following half-lives were determined:T _1/2(3045 keV)=3.7±0.3 ns in¹¹³Sb using the reaction¹⁰⁴Pd(¹²C,p2n) as well asT _1/2 (1322.8 keV)=3.5±0.3 ns,T _1/2(2779.8 keV) =0.50±0.15ns,T _1/2(2874.9 keV)<0.2 ns andT _1/2(3072.9 keV)<0.1 ns in¹¹⁷Sb using the¹¹⁶In(α, 2n) reaction. Three-quasiparticle configurations of the type πd _5/2ν(h_11/2 d _3/2) in^113,117Sb are found to dominate in the wave functions of the 19/2^? states at 3045 and 2780 keV in¹¹³Sb and¹¹⁷Sb, respectively. TheB(E2, 19/2^? → 15/2^?) values in^113–119Sb are discussed.